1. Technical Field
This invention relates generally to location determination using radio frequency devices, and more particularly to a method and apparatus for determining location of a radio frequency identifiable tag using reflected interferometry.
2. Background Art
Radio waves are commonly used with electronic transceivers built into miniaturized “tags” to identify objects. This practice is commonly known as “radio-frequency identification,” or “RFID,” and is often used in industry to determine the identity of a package or container of goods. For example, in supply chain management systems, a worker may use a handheld, electronic RFID “reader” to transmit a radio frequency signal at a package, crate, or shipping container. When the RFID tag receives the radio wave, electronic circuitry in the tag transmits a return radio wave that includes identification information. When the reader receives the return wave, by comparing the identification information to a database, the reader can deliver the database information corresponding to the package, crate, or shipping container to the reader.
One problem associated with many prior art RFID systems is that they require “line of sight” communication with the tag. Said differently, the worker must be able to see the tag and aim the reader directly at the tag for the radio waves to be received by the tag and reader respectively. Where, for example, a worker stands on the right side of a crate and the tag is affixed on the left side of the crate, the worker may not be able to read the tag without physically walking around the crate. Additionally, it can be advantageous in some applications to know the location of a tag in addition to its identity. Such line of sight systems are less than ideal for location determination.
A further problem with prior art solutions is that they tend to be application specific solutions. For example, certain tags only work with certain readers. Additionally, many readers are only capable of reading signals that are transmitted from the tag in response to the initial wave sent by the reader. Also, while a reader may be capable of cross-referencing identification data with a database, it may not be able to determine an accurate location of the tag. Such location determination may be important in some applications. Many prior art systems also rely on complex electronic circuits in tags that draw high amounts of current from a battery, thereby reducing the functional livelihood of the system.
There is thus a need for an improved radio-frequency system capable of efficiently and accurately determining the location of one or more tags in addition to their identity.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.